1. Field of the Invention
The present invention relates to a personal watercraft which navigates by the jet force of jet water through ejecting the jet water rearwards from a jet nozzle provided at a rear portion of a hull.
2. Description of the Related Art
Personal watercraft for navigating or planing on the waters of the sea and lakes are generally known. An example of such a personal watercraft is described in Japanese Patent Laid-open No. Hei 9-281132 and will be described below.
The personal watercraft includes an engine and a jet propeller driven by the engine which are disposed in a hull, and a steering nozzle provided at the rear end of the jet propeller. The jet propeller is driven by the engine, whereby an impeller of a water jet propeller is rotated, and water is sucked in through an intake port by the rotation of the impeller.
The water thus sucked in is ejected as jet water rearwards from the rear end of the steering nozzle. By the jet force of this jet water, the personal watercraft can plane in the condition where a front portion (bow) of the hull is floated up from the surface of water and can plane or navigate.
In order to efficiently eject the jet water from the rear end of the steering nozzle, it is preferable that the jet propeller is disposed close to the bottom of the hull. Meanwhile, as a driving engine for a personal watercraft, comparatively large engines are used in order to obtain the desired output. Therefore, the component around the crankshaft of the engine is large, and the crankshaft must be spaced upwards from the hull bottom.
Therefore, in order to dispose the jet propeller close to the hull bottom so as to efficiently eject the jet water, it is necessary to connect the components from the crankshaft to the jet propeller rectilinearly and to set the axis of the jet propeller rearwardly downwards.
On the other hand, the jet direction of the jet water ejected from the steering nozzle is desirably made to coincide with the axis of the jet propeller, in view of simplification of structure.
In addition, with the jet direction of the jet water ejected from the steering nozzle made to coincide with the axis of the jet propeller, it is possible to efficiently eject the jet water and to enhance the propulsion force.
However, in the above-mentioned personal watercraft, the jet direction of the jet water is rearwardly downwards, so that an upward lifting-up force is exerted on the stern. Therefore, when the sailing velocity is increased, the hull is put into a posture with its front portion lowered, causing the navigation resistance to be increased.
Of the conventional personal watercrafts, some have a structure in which the steering nozzle is disposed with a rearwardly upward gradient in order to reduce the navigation resistance. With the steering nozzle thus disposed with the rearwardly upward gradient, the stern of the hull can be lowered during navigation, and the hull can be maintained in a horizontal posture.
However, where the steering nozzle is disposed with the rearwardly upward gradient, the jet water from the jet propeller is deflected by the steering nozzle, so that the flow passage resistance is increased, resulting in a lowering of the propulsion force. In addition, where the steering nozzle is disposed with the rearwardly upward gradient, the constitution is complicated, and the number of component parts and the number of assembling steps are increased.
Accordingly, it is an object of the present invention to provide a personal watercraft in which the flow passage resistance is reduced, whereby jet water can be efficiently ejected, and a simpler constitution can be achieved.